This invention relates to a screw type disc brake device which is suitable for a vehicle, especially for a small type automotive vehicle such as a motorcycle, a snow-mobile and so forth. More specifically, the present invention relates to an improvement in a mechanical disc brake device wherein a male screw member of a relatively large screw lead having a brake operating lever fixed to the outer end thereof is screw-engaged with a caliper arm for supporting a movable friction pad and the thrust exerted by forward rotation of the male screw member by means of the brake operating lever is utilized as an urging force to bring the movable friction pad into firm pressure contact with the brake disc.
Generally, the disc brake device is provided with an automatic gap adjustment device for keeping the gap between the friction pad and the brake disc substantially constant at all times irrespective of the wear of the friction pad. When this automatic gap adjustment device is out of order, however, the prior art device has no means at all for adjusting the gap between the friction pad and the brake disc. This gap increases with increasing wear of the friction pad and increases the ineffective stroke of the brake operating lever.
To cope with the abovementioned problem, the first object of the present invention is to provide, in the abovementioned screw type disc brake device, a disc brake device which includes the automatic gap adjustment device for automatically adjusting the gap between the friction pad and the disc brake, as well as a device capable of manually adjusting the gap so that the gap can be properly adjusted by a simple manual adjustment, and the adjustment can be made at all times through a suitable actuation angle of the brake operating lever even when the automatic adjustment device is out of order.
In the disc brake device in general, further, the friction pad more or less experiences compressive deformation at the time of braking owing to the operation of a pad pressing device, and, as a result of the reaction, caliper arms of a brake caliper undergo elastic deformation that more or less spreads the caliper arms. The deformation of the kind described results in the apparent wear of the friction pad. If the automatic gap adjustment device is actuated in response to such apparent wear of the friction pad, this leads to so-called "over-adjustment", with the result that when the elastic deformation of the friction pad and brake caliper is restored upon releasing the brake, a sufficient gap no longer exists between the friction pad and the brake disc, whereby the friction pad gives rise to a strong drag phenomenon which is undesirable.
Accordingly, another object of the present invention is to provide a simple but effective automatic gap adjustment device which functions to prevent the "over-adjustment" in order to eliminate the abovementioned problem.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings which illustrate a presently preferred embodiment of the invention.